Adsorption And Desorption Of Suspended Sediment On Ammonia Nitrogen In The Wunonglong Hydropower Station On Lancang River

Coupling sediment with pollutants is one of the current hotspots within environmental sediment research.Suspended sediment is an important carrier for the migration and transformation of nitrogen,phosphorus and other pollutants in the water,so it is the main object of the study in water and sediment environment system.This study selects the Wunonglong hydropower Station as the research object.Suspended sediment samples were taken at sites of the Liutongjiang Hydrological Station at the tail of the Wunonglong reservoir,the upper and lower sections of the Dam in September 2019 for experiments.Analysis on sediment characteristics,and experimental study of sediment’s ammonia nitrogen adsorption and desorption effected by different sediment particle sizes and concentrations.Results are concluded as follows:（1）The suspended sediment particle sizes of the three sampling sites mainly range for 0～0.038 mm.The specific surface area,cumulative pore volume,and cumulative pore area of the suspended sediment decrease from upper,lower dam to hydrological station,and negatively correlate to the particle diameter.Suspended sediment particle size range of the hydrological station section is the widest,and the sediment concentration is the largest.The particle size>0.15 mm accounts for 9.15%,which is obviously different from the other two sampling sections.（2）The analysis results of the particle size parameters show that the three sampling sections were well sorted,and the partial attitude on the dam is nearly symmetrical.The other two sampling points are affected by the water velocity and hydrodynamic,Grain size distribution curve kurtosis look steep with obvious positive deviation,Grain size distribution curve at hydrological station is mainly flat.（3）The ammonia nitrogen adsorption equilibrium time（1h）of three suspended sediments is less than the desorption equilibrium time（9h）,indicating that the desorption process lags behind the adsorption process.Meanwhile,the equilibrium ammonia nitrogen adsorption capacity at lower dam is the largest,reaching 69.10 mg/kg.The quasi-first-order kinetic equation can better simulate the kinetic process of ammonia nitrogen adsorption at different sampling points（R~2=0.9546>0.9168）.The balance desorption amount of suspended sediment ammonia nitrogen at the dam section is the largest（60.07 mg/kg）,and the two kinetic equations have no obvious difference in simulating the desorption process.（4）During the isothermal equilibrium experiment,the ammonia nitrogen concentration within water phase increased from 0.5 mg/L to 5 mg/L,the balance adsorption and desorption capacity of suspended sediment ammonia nitrogen in each section also increased,and the balance desorption capacity of ammonia nitrogen in suspended sediment at upper dam was twice more than those at other two sections.（5）The adsorption capacity of ammonia nitrogen in sediment of different particle sizes increased with time,showing a trend of increasing-decreasing-increasing.The desorption capacity of ammonia nitrogen increased with time.When the suspended sand particle size changes from small to large,the amount of ammonia nitrogen adsorption and desorption gradually decreases.（6）Higher sediment concentrations lead to more adsorption and desorption of ammonia nitrogen,but sediment unit mass of the adsorption and desorption of ammonia nitrogen decreases.Under the same sediment concentration,the amount of ammonia nitrogen desorption is less than the that of ammonia nitrogen adsorption.This study reveals the characteristics of the suspended sediment in the Wulonglong hydropower Station and its adsorption and desorption of ammonia nitrogen,and can provide a scientific reference for management of water and sediment environment in the reservoir.